1. Field of the Invention
The present invention relates to a nitride semiconductor laser chip, and more particularly to a nitride semiconductor laser chip having a coating film formed on a resonator facet.
2. Description of Related Art
Nitride semiconductor laser chips employing a nitride semiconductor are used in high-density optical disc systems with high storage capacities, specifically as a light source for reading information from and writing information to BDs (Blu-ray Discs (a registered trademark)). In such high-density optical disc systems, for increasingly fast writing to discs with increasingly large numbers of layers, nitride semiconductor laser chips with high optical output have been sought eagerly.
On the other hand, recent years have seen many attempts to use nitride semiconductor laser chips not only as a light source in optical disc systems but also for lighting and in displays. Also in cases where nitride semiconductor laser chips are used for such purposes, demand is strong for nitride semiconductor laser chips with higher output.
Disadvantageously, however, it is known that when a nitride semiconductor laser chip is operated at high optical output, the resonator (cavity) facets deteriorate easily, their deterioration leading to low reliability. In increasing the output of a nitride semiconductor laser chip, therefore, it is essential to suppress deterioration of the resonator facets.
Accordingly, there have conventionally been proposed nitride semiconductor laser chips in which, to suppress deterioration of the resonator facets, a protective film (coating film) in a crystalline state is formed on the resonator facets. One example of such a nitride semiconductor laser chip is proposed in JP-A-2008-182208.
Inconveniently, however, even with the conventional technology proposed in JP-A-2008-182208, sufficient reliability is not obtained in cases where nitride semiconductor laser chips are operated at such high optical output as sought in these days.